Goethe(1)

Goethe's youth was emotionally hectic to the point that he sometimes feared for his reason. He was recognized as a leading figure in the Sturm und Drang, which celebrated the energetic Promethean restlessness of spirit as opposed to the ideal of calm rationalism of the Enlightenment. Goethe's poem 'Prometheus', with its insistence that man must believe not in gods but in himself, might be seen as a motto for the whole movement. After a relaxing trip to Switzerland, Goethe made a decisive break with his past. In 1775 he was welcomed by Duke Karl August into the small court of Weimar, where he worked in several governmental offices. Occasionally he read aloud his texts to a selected group of persons - among them the Duke and the two Duchesses. To his disappointment a dog-trainer was also allowed to amuse in the court theatre.
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I have a sole question on the above. Would you kindly answer the following question?


What is the meaning of the words 'feared for his reason' in the first sentence?